My Jailbroken iphone?

i need very serious help because i wanted to jailbreak my ipod touch but the first time i did it with blackra1n it put me on a screen were it appeared itunes logo and an usb i wanted to know how can i jailbreak it again and then never get that thing again and if there is no way i can do it tell me how to get rid of that i already fixed it but thats because i took it to mac stor